A better understanding of the molecular mechanisms of assembly of some viruses

A team from the Laboratoire de Physique des Solides [Laboratory of Solid-State Physics] (Univ Paris-Sud/CNRS), also involving researchers from Institut de Biologie Intégrative de la Cellule [Institute of Integrative Biology of the Cell] (Univ Paris-Sud/CNRS/CEA), Laboratoire Léon Brillouin (CNRS/CEA) and the European Synchrotron Radiation Facility, has solved the assembly dynamics of a plant virus which has a 20-faced or icosahedral shell. They monitored the spontaneous reconstitution of the virus from purified proteins and genomic RNA by a sophisticated method of X-ray scattering. This study contributes to a better understanding of molecular mechanisms of assembly of a large class of viruses, namely, icosahedral RNA viruses, in order to develop therapeutic strategies to block their replication.

The cowpea chlorotic mottle virus (CCMV) is an RNA virus that infects a variety of bean. It has a shell, also called a capsid, made up of 90 protein sub-units arranged in an icosahedral structure, i.e. with 20 faces. The RNA molecules encoding the genome necessary for viral replication are enclosed in the capsid. The virus’ survival is partly based on its ability to self-assemble quickly and flawlessly in the host cell. Very few experimental measurements are currently available because of the difficulty in detecting biological molecules over a large range of timescales.

The virus was reconstituted from purified protein and genomic RNA sub-units, and its self-assembly was monitored by an X-ray scattering method with a synchrotron source. An empty capsid assembles sequentially and requires precise positioning of the sub-units during the process. For a complete virus, however, the genome acts as an assembly medium and captures in less than a second a large number of sub-units to form a disordered complex. The latter self-organises over a long time while continuing to capture missing sub-units, and gives rise to a protective capsid. This mechanism would be advantageous, both to quickly combine the basic virus components, but also to ensure selectivity of the genome and correct possible assembly errors.

Molecular representation of CCMV on a grassy background

Contact: Guillaume Tresset (guillaume.tresset @ u-psud.fr)

Unit: Laboratoire de Physique des Solides, UMR 8502

Team’s website: http://www.equipes.lps.u-psud.fr/sobio

Reference: M. Chevreuil, D. Law-Hine, J. Chen, S. Bressanelli, S. Combet, D. Constantin, J. Degrouard, J. Möller, M. Zeghal, G. Tresset, Nat. Commun. 2018, 9, 3071.